The invention relates to an arrangement for the web threading of a multi-roll calender of a paper/board or finishing/converting machine, which calender comprises a number of rolls formed into a roll stack, and a number of lift-out rolls, which are arranged in such a way that the web being treated travels from one calender nip to another via a lift-out roll.
With paper machines, the trend has for long been to close open transfers in order to improve runnability. As a result of online calendering, the first open transfers are between the dryer section of the paper machine and the calender, and in the set of rolls of the calender.
Nowadays it is known that many web breaks take place precisely at the calender. These can be eliminated quite efficiently by closing the web threadings inside the calender and between the dryer section and the calender. Closing the web threading before and after the calender is not in any way extraordinary. The problem is instead how to accomplish functional closing of the web threading in the set of calender rolls.
The web threadings of the calender will in future have to be closed due to, among other things, higher running speeds, whereby the loads on the web will increase due to the optimisation of draws, or in general to improve time efficiency.
One solution for closing the web threading of a calender is disclosed in the publication U.S. Pat. No. 4,552,620. In it, the belt used for closing the web threading is looped through the calender nips (see appended FIG. 1). The paper web travels through each nip between the belt and the roll. The web is not supported in a completely satisfactory manner when it travels through the calender. The situation can be somewhat improved by applying the known solution to a calender of the above-mentioned type which is equipped with lift-out rolls.